A common method of molding composites, known as the resin transfer molding process, involves placing a structure of reinforcing fibers, for example glass, carbon of KEVLAR, into a mold and then injecting a liquid resin into the mold so that it penetrates through the entire reinforcing structure. The resin then cures producing a resin/fiber composite with good mechanical properties and relatively low weight. The final mechanical properties depend on the type of reinforcing fiber and resin employed. A conventional arrangement for transferring resin from a resin injection machine into the fibers in a mold is shown in FIG. 1 of the accompanying drawings. The nozzle from the resin injection machine is clamped to the injection port of the mold and pressurized resin is fed from the injection machine, entering the reinforcing fibres at the injection port. On large moldings more than one port may be used by this presents problems as the resin cures in the feed system and means must be provided for removing the cured resin.
In recent years there has been a significant increase in the complexity of moldings made by the resin transfer molding process brought about by the introduction of preforming which allows the assembly of complex configurations of reinforcing fibers together with, for example, the use of foamed plastics material inserts. Structures may now be produced of the type shown in FIG. 2 of the accompanying drawings where two skins are separated by foam inserts and interconnecting members are included. In order to inject resin successfully it is preferable to inject into both skins simultaneously. The mold used for such a component would, as illustrated, normally be split in such a way that the two skins lie on alternative mold faces. Therefore injecting resin into such a component requires two injection ports as shown in FIG. 2. In practice this is difficult to achieve since either two injection guns would be required or the resin would have to be gated to each port, or one port may be used but located at one edge thereby lengthening the injection cycle time.
Our PCT publication No. WO89/00495 provides a method of molding complex shapes having a skin portion to be injected with the resin and a core portion impenetratable to resin which comprises providing a core portion bearing one or more galleries placing same in a suitable mold and injecting resin into the gallery whereby it is rapidly transmitted to all portions of the skin.
The use of a gallery or galleries in the otherwise resin-impermeable core allows resin to be ducted to wherever needed according to the mold configuration by employing a single resin injection nozzle. The injection nozzle is inserted through the injection port through one skin of the article to be molded into the gallery thereof. On completion of the injection cycle the nozzle is removed prior to the resin curing and the injection port is plugged. The method of the invention allows very complex structures to be produced and cycle times reduced.
We have now found that a similar effect can be obtained by providing galleries in the inner surface of the mold rather than the core.